The goal of this laboratory is to understand as much as possible about the function and control of enzyme systems which are involved in either the repair of chemical damage or the production of biological consequences from this damage. In higher organisms, one of these biological consequences is malignant transformation. It is still not clear precisely why chemical damage leads to transformation, but the answere must be found somewhere in the enzymatic reactions which occur within a cell following DNA damage. The understanding of carcinogenesis thus requires the understanding of these reactions. The specific goal of this project is to investigate the control and function of the mismatch repair system and to determine its role in modulating the mutagenic effects of alkylating agents. Mutant strains of Escherichia coli which are defective in this process will be isolated. These mutants will be produced by insertion of a fefective Mu phage (Mu-dl) into each of the various operons coding for a component of the mismatch repair system. These insertions produce an operon fusion in which the production of the readily detectable protein Betha-galactosidase will be controlled by the promoter for the mismatch repair gene. Thus, agents which cause induction or repression of the synthesis of mismatch repair proteins can be readily monitored by assaying Beta-galactosidase. If any of these genes prove to be regulated, they will be cloned and the sequence of their regulatory region determined for comparison with other operons which code for DNA repair functions. Along with the studies on the control of mismatch repair, this project will attempt to determine the role of mismatch repair in reducing alkylation induced mutagenesis; and its role, if any, in fixing these mutations. To understand this role, experiments have been designed which will probe the kinds of base pairs recognized by these enzymes and the types of sequences in which they can function. The studies should give insignt into the function of the various components of the mismatch repair system and their function in other cellular processes.